Well stimulation tool and method of using same

ABSTRACT

A well stimulation tool is connected to a top of a tubing hanger in a well to be stimulated. The well stimulation tool includes an adapter pin that connects to the tubing hanger. The adapter pin is connected to a mandrel that reciprocates through a top end of an adapter spool, which is mounted to a tubing head spool that supports the tubing hanger. A high-pressure valve is mounted to a top end of the mandrel. High-pressure fluids are pumped through the high-pressure valve, the mandrel, the adapter pin, the tubing hanger, and a production tubing into the well.

TECHNICAL FIELD

The present application claims priority to Canadian Application No.2,364,151, filed with the Canadian Intellectual Property Office on Nov.29, 2001.

The invention relates to the stimulation of oil and gas wells to improveproduction and, in particular, to a well stimulation tool used todeliver high-pressure fluids through a production tubing of a well inorder to acidize and/or fracture subterranean formations with which thewell communicates.

BACKGROUND OF THE INVENTION

It is well known that many oil and gas wells require stimulation inorder to increase production either as a part of well completion, or asa part of well workover. Well stimulation involves the pumping of fluidsunder high pressure into the annulus of the well in order to break upsubterranean formations and release hydrocarbons into the wellbore,where they can be extracted to the surface. Since it is generally noteconomically feasible to manufacture wellhead equipment that canwithstand extreme pressures, the wellhead must be isolated or removedduring well stimulation in order to prevent potential damage and/orinjury.

One method of stimulating a well is to pump high-pressure fluids down aproduction tubing suspended in the well. To accomplish this, theproduction tubing is plugged and the wellhead is removed from the well.An extension is then screwed into the top of the tubing hanger andhigh-pressure fluids are pumped through a high-pressure valve thatcommunicates with a top of the extension. A high-pressure adapter ofthis type is described in U.S. Pat. No. 5,103,900 that issued on Apr.14, 1992 to McLeod et al., and entitled HIGH PRESSURE ADAPTER FORWELL-HEADS. McLeod et al. describe an improvement to the McEvoy PSTadapter and pack-off nipple in which vent ports are added to the McEvoytubing head adapter to comply with American Petroleum Institute (API)regulations respecting elevations in pressure rating between adjacentadapters.

The McEvoy PST adapter and McLeod et al.'s improvements to it sufferfrom several disadvantages, however. First, each adapter must beconstructed for a specific size of production tubing. Consequently, atleast one adapter must be kept in stock for each size of productiontubing that is to be serviced. Second, the flow path of high-pressurefluids is interrupted by an internal bore in the tubing head adapter.The internal bore provides a space where eddy currents develop in thehigh-pressure fluids. The eddy currents tend to cause abrasive wellstimulation fluids to “wash out” a top end of a pack-off nipple thatconnects to the tubing hanger. As is well understood in the art, damagecaused by wash out can cause dangerous pressure leaks.

There therefore exists a need for a well stimulation tool that permitshigh-pressure fluids to be safely pumped down the production tubing of ahydrocarbon well.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a well stimulationtool that permits high-pressure fluids to be safely pumped down theproduction tubing of a hydrocarbon well.

It is a further object of the invention to provide a well stimulationtool that is quickly and easily mounted to an exposed tubing hanger of ahydrocarbon well.

The invention therefore provides a well stimulation tool for stimulatinga well having a tubing head mounted to a casing spool of the well and aproduction tubing suspended from a tubing hanger in the tubing head. Thewell stimulation tool comprises an adapter spool having a bottom flangeadapted for connection to one of a tubing head and a blowout preventermounted to the tubing head. The adapter spool has a top end adapted toreceive a mandrel that can be reciprocally moved through a packing thatsurrounds the mandrel and is retained in a packing cavity in the top endof the adapter spool. The top end of the adapter spool further includesthreads for securing a lockdown nut that covers the packing andsurrounds an outer periphery of the mandrel.

The mandrel includes a mandrel top end having a flange adapted for theconnection of a high-pressure valve, and a mandrel bottom end having athread for the connection of an adapter pin. The adapter pin has a topend with threads for connecting the adapter pin to the mandrel bottomend. The adapter pin also has a bottom end with threads for connectingthe adapter pin to the top end of a tubing hanger.

The well stimulation tool preferably further includes a high-pressureflange adapted to be mounted to a top of the high-pressure valve. Thehigh-pressure flange has a pressure flange bottom end adapted forconnection to a top flange of the high-pressure valve. The high-pressureflange also has a top end that is threaded for connection to ahigh-pressure line for injecting high-pressure well stimulation fluidsinto the well.

In accordance with one embodiment of the invention, The well stimulationtool further comprises a lifting head assembly including a first memberand a second member. The first member has a bottom end adapted to beconnected to the high-pressure flange. The second member has means forconnecting a hoist to the well stimulation tool. When the lifting headassembly is connected to the combination of the high-pressure flange,high-pressure valve, the adapter spool, the mandrel and the adapter pin,and hoisted above the well, the adapter pin extends below the bottomflange of the adapter pin to facilitate the installation of the wellstimulation tool to the tubing hanger.

The lifting head assembly includes a hollow cylinder having a liftinghead top end and lifting head bottom end. The lifting head bottom endincludes an aperture. A lifting sub having a top end, which reciprocatesfreely within the hollow cylinder but cannot pass through the aperturein the bottom end, is adapted to connect to a top end of thehigh-pressure flange. A lifting eye is affixed to the lifting head topend.

The lifting head further comprises opposed, radially extending lift armsadjacent the lifting head bottom end, the lift arms respectivelyincluding a lift eye located near an outer end thereof. The lockdown nutalso comprises opposed, radially extending lift arms respectivelyincluding a lift eye located near an outer end thereof. First and secondlifting cables interconnect the lift arms of the lift head and thelockdown nut. Consequently, when the well stimulation tool is liftedusing the lifting eye affixed to the top end of the lifting head, thelifting sub top end moves downwardly within the hollow cylinder and thelifting cables bear the weight of the lockdown nut and the adapterspool. As a result, the mandrel is stroked down through the adapterspool and the adapter pin is extended beneath the bottom flange of theadapter spool to permit the adapter pin to be connected to, ordisconnected from, the top end of the tubing hanger.

The invention further provides methods for completing and stimulatingoil and gas wells.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a cross-sectional view of a well stimulation tool inaccordance with one embodiment of the invention;

FIG. 2 is a cross-sectional view of a well stimulation tool connected toa high-pressure valve and in a suspended position for installation onthe well, in accordance with another embodiment of the invention;

FIG. 3 is a cross-sectional view of the well stimulation tool with thehigh-pressure valve shown in FIG. 2 installed on the well;

FIG. 4 is a detailed cross-sectional view of a lifting head assembly anda high-pressure flange used with the well stimulation tool shown inFIGS. 2 and 3;

FIG. 5 is a schematic cross-sectional view of the well stimulation toolshown in FIGS. 2 and 3 with a lubricator that is being used to retrievea plug from a production tubing so that the well stimulation tool can beused to stimulate a hydrocarbon well, without a blowout preventer;

FIG. 6 is a schematic cross-sectional view of the well stimulation toolillustrated in FIG. 5 with the lubricator removed and a high-pressureline connected to the well stimulation tool; and

FIG. 7 is a schematic cross-sectional view showing the well stimulationtool shown in FIGS. 2 and 3 with an elongated adapter pin used tostimulate a hydrocarbon well through a blowout preventer.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a well stimulation tool that permitshigh-pressure fluids to be pumped into the well through a productiontubing string suspended in the well by a tubing hanger. The toolfacilitates a fast, sure connection to the tubing hanger.

FIG. 1 is a cross-sectional view of the well stimulation tool inaccordance with one embodiment of the invention. The well stimulationtool, generally indicated by reference numeral 10, includes an adapterspool 12. A mandrel 14 is received in an axial passage 16 in the adapterspool 12. The axial passage 16 includes a throat region 20 and anadapter pin docking region 22. The throat 18 retains a steel packingwasher 24. High-pressure packing 26, such as a chevron packing, isretained above the steel packing washer 24. The high-pressure packing 26closely surrounds and provides a high-pressure seal around the mandrel14, in order to ensure that well fluids do not escape to the atmospherewhen the adapter spool 12 is mounted to one of a tubing head spool 102,as shown in FIG. 3, and a blowout preventer 120 mounted to the tubinghead spool 102, as shown in FIG. 7. The high-pressure packing 26 isretained by a gland nut 28. A lockdown nut 30 threadedly engages aspiral thread on an outer periphery of the top end of the adapter spool12. A top wall of the lockdown nut 30 projects inwardly to cover thegland nut 28 in order to ensure that the gland nut 28 is not stripped byfluid pressures exerted on the high-pressure packing 26, while beingradially spaced apart from the outer periphery of the mandrel 14 inorder to permit free reciprocation of the mandrel 14 within the axialpassage 16 of the adapter spool 12.

An adapter pin 32 has an axial bore 34, and includes a top end thatthreadedly engages an external spiral thread on the bottom end of themandrel 14, and a bottom end sized to match a size of a productiontubing (not shown) in the well, for example, {fraction (3/8″, 27/8)}″ or3½″. The adapter pin 32 is equipped with any required thread pattern onthe bottom end to match that of a tubing hanger 106 (FIG. 3) from whichthe tubing is suspended in the well. Typically, the tubing hanger hasE.U.E. threads, which are well known in the art. The adapter pin 32 isinterchangeable to permit the tool 10 to be connected to different sizesof tubing hangers. Ring seals 36 are incorporated in the adapter pin 32to provide a seal between the mandrel 14 and the adapter pin 32 toprevent fluid leakage when high-pressure fluid flows through a centralpassage 38 of the mandrel 14 and the central bore 34 of the adapter pin32.

The mandrel 14 further includes a stud pad 40 having threaded bores 42for receiving studs for mounting a high-pressure valve 64 (FIG. 2)thereon. A bottom flange 44 of the adapter spool 12 includes mountingbores 46 for bolting the adapter spool 12 to a top of another spool,such as a blowout preventer or a tubing head spool. An annular groove 48is also provided in the bottom flange 44 of the adapter spool 12 and thestud pad 40 of the mandrel 14 respectively, for receiving a gasket seal(not shown) when the tool 10 is connected between a high-pressure valveand one of the tubing head spool and a blowout preventer mounted to thetubing head spool.

The reciprocation of the mandrel 14 within the axial passage 16 of theadapter spool 12 is limited in a downward direction by the stud pad 40and in an upward direction by the adapter pin 32, which has a diametergreater than that of the throat region 20, and smaller than that of thedocking region 22 of the adapter spool 12. Thus, the mandrel 14 canreciprocate within the adapter spool 12 but cannot be removed from theadapter spool 12 when the adapter pin 32 is connected to the mandrel 14.

The adapter spool 12 further includes a bleed-off port 50 which isclosed by a needle valve 52, having a pressure rating of at least 10,000Psi. The needle valve 52 is left open during well stimulation treatmentso that any pressure leak is readily detected.

When the lockdown nut 30 is connected to a service rig or boom truck(neither one shown) and the well stimulation tool 10 is hoisted aboveone of a tubing head spool and a blowout preventer mounted on the tubinghead spool, the mandrel 14 moves downward under its own weight and theadapter pin 32 extends beneath the bottom flange 44 of the adapter spool12. Thus, the adapter pin 32 can be visually guided into a connectionwith the tubing hanger in the tubing head spool, or inserted through theblowout preventer mounted on the tubing head spool to be connected tothe tubing hanger in the tubing head spool. After the adapter pin 32 isconnected to the tubing hanger, the adapter spool 12 is lowered topermit it to be mounted to the top of the tubing head spool, or the topof the blowout preventer. This operation will be further described belowwith reference to FIGS. 2 and 3.

FIGS. 2 and 3 illustrate another embodiment of the invention, generallyindicated by numeral 11 which includes the well stimulation tool 10illustrated in FIG. 1, and further includes a high-pressure flange 54and a lifting head assembly 56.

The high-pressure flange 54 and the lifting head assembly 56 areillustrated in detail in FIG. 4. The high-pressure flange 54 includes apressure flange top end 58 having a spiral thread on an outer peripherythereof for connection of the lifting head assembly 56, a wirelinelubricator, or a high-pressure fluid line, as will be further describedbelow with reference to FIGS. 5-7. The high-pressure flange 54 alsoincludes a bottom flange 60 with mounting bores 62 that extendtherethrough for bolting the high-pressure flange 54 to a top of thehigh-pressure valve 64, as shown in FIGS. 2 and 3. An annular groove 66is provided in the bottom flange 60 for receiving a gasket seal (notshown) when the high-pressure flange 54 is mounted to the high-pressurevalve 64 shown in FIGS. 2 and 3. An axial passage 68 extends through thehigh-pressure flange 60 for fluid communication with the high-pressurevalve 64.

The lifting head assembly 56 includes a lifting head 70 and a liftingsub 72. The lifting head 70 includes a hollow cylinder 74, which has atop end 76 and a bottom wall 78 that is preferably threadedly secured toa bottom end thereof. The lifting sub 72 has a side wall 80,interconnecting a lifting sub bottom end 82 and a lifting sub top end84. The lifting sub top end 84 has a diameter slightly smaller than aninner diameter of the cylinder 74, and greater than an outer diameter ofthe side wall 80 so that the lifting sub top end 84 is slidingly guidedwithin the cylinder 74 when the side wall 80 of the lifting sub 72reciprocates through an axial aperture 86 in the bottom wall 78 of thecylinder 74. The lifting sub top end 84 is preferably threadedlyconnected to the top end of the side wall 80. The lifting sub bottom end82 has a diameter greater than that of the aperture 86 of the bottomwall 78, so that the aperture 86 of the bottom wall 78 permits freereciprocation of the lifting sub 72 within the cylinder 74, but preventsthe lifting sub 72 from being removed in either direction from thecylinder 74. The lifting sub bottom end 82 further includes a bottomshoulder 88 that rotatably engages a hammer union 90, which threadedlyengages the spiral thread on the outer periphery of the top end 58 ofthe high-pressure flange 54.

The lifting head 70 further includes a lifting eye 92, which is used tomanipulate the well stimulation tool 11. The lifting eye 92 is affixedto the top end of the cylinder 74. The lifting head 70 is provided witha mechanism for connecting the adapter spool 12 shown in FIGS. 2 and 3which, in this embodiment, includes two opposed radially extending liftarms 94 adjacent to the bottom end of the lifting head 70. Each of thelift arms 94 includes a lift eye 96 located near an outer end thereof.The lockdown nut 30 shown in FIGS. 2 and 3 also includes two opposedradially extending lift arms 94′, with lift eyes 96′ in their respectiveouter ends. Corresponding lift arms 94 and 94′ on the respective lifthead 70 and the lockdown nut 30 are interconnected by lifting cables 98using removable connectors, such as a clevis 100 that is well known inthe art.

A typical well is completed for stimulation by running a productiontubing into the well. The production tubing is generally run into thewell through a blowout preventer mounted to the top of the tubing headspool. After the production tubing is run into the well, a tubing hangeris connected to a top of the production tubing, and the tubing hanger isinserted through the blowout preventer and into tubing head spool whereit is secured in a manner well known in the art. In well completion orwell workover, which require a well stimulation procedure, the wellstimulation tool 10 or 11 in accordance with the invention, can be usedto direct high-pressure stimulation fluids into the well through theproduction tubing. A method of using the well stimulation tool 10 or 11is described below.

The stimulation of a hydrocarbon well from which a blowout preventer hasbeen removed is illustrated in FIGS. 2, 3, 5 and 6. As an example, thewell stimulation tool. 11 is used to illustrate the features andadvantages of the present invention. A boom truck or a rig (not shown)is used to hoist the combination of the well stimulation tool 11 and thehigh-pressure valve 64 by connecting the hoist (not shown) to thelifting eye 92 at the top of the lifting head 70. When the combinationof the well stimulation tool 11 and the high-pressure valve 64 is liftedusing the lifting eye 92, the lifting cables 98 support the weight ofthe lockdown nut 30 and the adapter spool 12. Consequently, the weightof the high-pressure valve 64, the mandrel 14, the high-pressure flange54 and the lifting sub 72 causes the mandrel 14 to stroke down throughthe packing 26 in the adapter spool 12 and the lifting sub 72 to strokedown through aperture 86 in the lifting head 70, so that the adapter pin32 extends beneath the bottom flange 44 of the adapter spool 12 to anextent, as shown in FIG. 2, which facilitates the connection of theadapter pin 32 to a tubing hanger 106 in the tubing head spool 12 shownin FIG. 3.

The combination of the well stimulation tool 11 and the high-pressurevalve 64 illustrated in FIG. 2 is suspended over a wellhead to which atubing head spool 102 (see FIG. 3) is mounted. A production tubing 104is suspended from the tubing hanger 106, which is secured in the tubinghead spool 102. The combination of the well stimulation tool 11 and thehigh-pressure valve 64 is lowered and rotated to threadedly engage thebottom end of the adapter pin 32 with the top end of the tubing hanger106 shown in FIG. 3. It should be understood that the adapter pin 32 isvisible to permit it to be visually guided into a connection with thetubing hanger 106. This facilitates the connection and helps to ensurethat the threads on the adapter pin are not damaged. After the adapterpin 32 is securely connected to the tubing hanger 106, the boom truck orrig is operated to further lower the combination of the well stimulationtool 11 and the high-pressure valve 64, which causes the adapter spool12, the lockdown nut 30 and the lifting head 70 to move downwardly untilthe adapter spool 12 rests on the top of the tubing head spool 102 whenthe high-pressure valve 64 with the remaining parts of the wellstimulation tool 11 are supported by the tubing hanger 106, asillustrated in FIG. 3. The bottom flange 44 of the adapter spool 12 andthe top flange of the tubing head spool 102 are then bolted together andthe installation of the well stimulation tool 11 with the high-pressurevalve 64 is thereby completed.

Subsequently, the respective clevises 100 that connect the liftingcables 98 to the lockdown nut 30 are released. The hammer union 90 isalso released. Thus, the lifting head assembly 56 with the hammer union90 can be removed from the top end of the high-pressure flange 54. Asillustrated in FIG. 5, a lubricator that is well known in the art,typically a wireline lubricator 108 (which is schematicallyillustrated), is then connected to the top end of the high-pressureflange 54. After the wireline lubricator 108 is mounted to the top endof the high-pressure flange 54, the high-pressure valve 64 is opened anda wireline 110 is run into the production tubing 104 to retrieve aretrievable plug 112 that is normally set in the production tubing 104before it is run into the well. The high-pressure valve 64 is thenclosed and the wireline lubricator 108 is removed.

Thereafter, a high-pressure line 114, as illustrated in FIG. 6, isconnected to the top end of the high-pressure flange 54 using a hammerunion 116 in a manner well known in the art. The high-pressure valve 64is then opened and high-pressure fluids, such as acidizing or fracturingfluids, are pumped through the high-pressure flange 54, thehigh-pressure valve 64, the mandrel 14, the adapter pin 32, the tubinghanger 106, the production tubing 104, and into the well.

After the well stimulation procedure is complete, the stimulation fluidsare “flowed back” through the well stimulation tool 11 and thehigh-pressure valve 64. When the flow-back process is complete, thehigh-pressure valve 64 is closed and the high-pressure line 114 isdisconnected from the high-pressure flange 54. If the well containsnatural pressure, the tubing must be plugged once again before the wellstimulation tool 11 and the high-pressure valve 64 can be removed.Consequently, the wireline lubricator 108 is mounted again to thehigh-pressure flange 54 as shown in FIG. 5 and the wireline 110 is rundown to reset the removable plug 112 in the production tubing 104.

After the plug 112 is set, the wireline 110 is retrieved and then thewireline lubricator 108 is again removed from the high-pressure flange54.

After the wireline lubricator 108 is removed, the lifting head assembly56 shown in FIG. 4 is hoisted back to the top end of the high-pressureflange 54. The lifting cables 98 are connected to the respective liftingeyes 96′ in the lockdown nut 30 by re-inserting the devises 100, and thelifting sub 72 is connected to the top end of the high-pressure flange54 using the hammer union 90. The adapter spool 12 is then unbolted fromthe tubing head spool 102 and a hoist (not shown) is connected to thelifting eye 92 at the top of the lifting head 70. The lifting head 70 ishoisted to expose the adapter pin 32, the bottom end of which is thendisconnected from the tubing hanger 106. Thereafter, the entire wellstimulation tool 11 together with the high-pressure valve 64 is hoistedonto a service truck (not shown).

After the well stimulation tool 11 with the high-pressure valve 64 isremoved, a wellhead (not shown) is mounted to the tubing head spool 102.The wireline lubricator 108 is then mounted to the top of the wellheadand the wireline 110 is run into the production tubing string toretrieve the plug 112. The well is then ready for the production ofhydrocarbons.

It should be noted that after the tubing hanger 106 is secured in thetubing head spool 102 in a well completion, a blowout preventer that wasrequired for the well completion procedure may remain on the wellhead.It should be understood, however, that the well stimulation tool 10 or11 in accordance with the invention can be used with or without ablowout preventer in place.

FIG. 7 illustrates the well stimulation tool 11, which is assembled withthe high-pressure valve 64 and is mounted on the top of a blowoutpreventer 120. The blowout preventer 120 is mounted on the top of thetubing head spool 102. In this case, either the adapter pin 32 or themandrel 14 must be longer than that of a similar well stimulation tool11 used for a wellhead from which a blowout preventer is removed, suchas the embodiment illustrated in FIGS. 2, 3, 5 and 6. In the embodimentillustrated in FIG. 7, a longer adapter pin 32′ replaces the adapter pin32 shown in FIGS. 2, 3, 5 and 6. The use of the well stimulation tool 11to stimulate a hydrocarbon well to which a blowout preventer 120 shownin FIG. 7 is mounted is similar to the procedure described withreference to FIGS. 2, 3, 5 and 6, and is therefore not redundantlydescribed.

As will be understood by those skilled in the art, the well stimulationtool 10 in accordance with the invention can be used without the liftinghead assembly. In that case, the adapter spool 12, the mandrel 14 andthe adapter pin 32 are mounted to a top of the tubing head spool 102shown in FIG. 6, as described above. After they are installed, ahigh-pressure valve 64 shown in FIG. 6 is mounted to the top flange ofthe mandrel 14 and a high-pressure line 114 shown in FIG. 6 is connectedto a top of the high-pressure valve 64. The high-pressure flange 54described above may also be used to connect the high-pressure line tothe high-pressure valve. It should be further understood that thelockdown nut 30 shown in FIG. 1 may include lift arms 94′ (FIG. 2) withlift eyes 96′ to which cables are connected for hoisting the wellstimulation tool 10 into position over the wellhead, or removing thewell stimulation tool from the wellhead.

The embodiments of the invention described above are therefore intendedto be exemplary only. Consequently, the scope of the invention isintended to be limited only by the scope of the appended claims.

I claim:
 1. A well stimulation tool for stimulating a well having atubing head spool and a production tubing suspended from a tubing hangerin the tubing head spool, comprising: an adapter spool having a bottomflange adapted for connection to one of the tubing head spool and ablowout preventer mounted to the tubing head spool, and a top endadapted to receive a mandrel that can be reciprocally moved throughpacking that surrounds the mandrel and is retained in a packing cavityin the top end, the top end further including threads for securing alockdown nut that covers the packing and surrounds an outer periphery ofthe mandrel; the mandrel having a mandrel top end and a mandrel bottomend, the mandrel top end having a flange adapted for the connection of ahigh-pressure valve, and the mandrel bottom end having a thread for theconnection of an adapter pin; and the adapter pin having an adapter pintop end and an adapter pin bottom end, the adapter pin top end havingthreads for connecting the adapter pin to the mandrel, and the adapterpin bottom end having threads for connecting the adapter pin to a topend of the tubing hanger.
 2. A well stimulation tool as claimed in claim1, further comprising: a high-pressure flange adapted to be mounted to atop of the high-pressure valve, the high-pressure flange having apressure flange top end and a bottom flange, the bottom flange beingadapted for connection to a top flange of the high-pressure valve andthe pressure flange top end being threaded for connection of ahigh-pressure line for injecting high-pressure well stimulation fluidsinto the well.
 3. A well stimulation tool as claimed in claim 1, furthercomprising a lifting head assembly having a first member that includes abottom end adapted to be connected to the high-pressure flange, and asecond member having means for connecting the lift head to a hoist, inorder to permit the well stimulation tool to be lifted for installationon, or removal from, the one of the tubing head and the blowoutpreventer.
 4. A well stimulation tool as claimed in claim 3, wherein thefirst member comprises a lifting sub having a lifting sub top end, alifting sub bottom end and a cylindrical side wall that interconnectsthe lifting sub top end and the lifting sub bottom end, and the secondmember comprises a lifting head comprising a hollow cylinder having alifting head top end and a lifting head bottom end, the lifting headbottom end including an aperture; and the lifting sub top end isreceived in the hollow cylinder and freely reciprocates therein, butcannot pass through the aperture in the lifting head bottom end, and thelifting sub bottom end is adapted to be connected to the pressure flangetop end.
 5. A well stimulation tool as claimed in claim 4, wherein thelifting head assembly further comprises a lifting eye affixed to thelifting head top end.
 6. A well stimulation tool as claimed in claim 4,wherein the lifting head further comprises opposed, radially extendinglift arms adjacent the lifting head bottom end, the lift arms, eachincluding a lift eye located near an outer end thereof.
 7. A wellstimulation tool as claimed in claim 6, wherein the lockdown nut furthercomprises opposed, radially extending lift arms, each including a lifteye located near an outer end thereof.
 8. A well stimulation tool asclaimed in claim 7, further comprising: first and second lifting cables,the first lifting cable having opposed ends respectively connected to acorresponding lift eye in one of the lift arms of the lifting head and alift eye in one of the lift arms of the lockdown nut, and the secondlifting cable having opposed ends respectively connected to acorresponding lift eye in the other of the lift arms of the lifting headand a lift eye in the other of the lift arms of the lockdown nut;whereby when the well stimulation tool is lifted using the lifting eyeaffixed to the lifting head top end, the lifting sub top end movesdownwardly within the hollow cylinder and the lifting cables bear theweight of the lockdown nut and the adapter spool, so that the mandrel isstroked down through the adapter spool and the adapter pin is extendedbeneath the bottom flange of the adapter spool to permit the adapter pinto be connected to, or disconnected from, the top end of the tubinghanger.
 9. A well stimulation tool as claimed in claim 1, wherein theadapter spool further comprises a pressure bleed port.
 10. A wellstimulation tool as claimed in claim 9, wherein the pressure bleed portis closed by a high-pressure needle valve.
 11. A method of stimulating ahydrocarbon well comprising steps of: connecting a well stimulation toolto a top of a tubing hanger in a tubing head spool of the well, the wellstimulation tool comprising: an adapter spool having a bottom flangeadapted for connection to the tubing head spool, and a top end adaptedto receive a mandrel that can be reciprocally moved through packing thatsurrounds the mandrel and is retained in a packing cavity in the topend, the top end further including threads for securing a lockdown nutthat covers the packing and surrounds an outer periphery of the mandrel;the mandrel having a mandrel top end and a mandrel bottom end, themandrel top end having a flange adapted for the connection of ahigh-pressure valve, and the mandrel bottom end having a thread for theconnection of an adapter pin; and the adapter pin having an adapter pintop end and an adapter pin bottom end, the adapter pin top end havingthreads for connecting the adapter pin to the mandrel, and the adapterpin bottom end having threads for connecting the adapter pin to a top ofthe tubing hanger; mounting a high-pressure valve to the flange at themandrel top end; connecting a high-pressure line to a top of thehigh-pressure valve; opening the high-pressure valve; and pumpinghigh-pressure fluid through the high-pressure line to stimulate thehydrocarbon well.
 12. A method as claimed in claim 11 wherein, after thestep of mounting the high-pressure valve to the flange and beforeconnecting the high-pressure line, the method further comprises stepsof: mounting a wireline lubricator to a top of the high-pressure valve;opening the high-pressure valve running in a wireline and retrieving aplug from a production tubing suspended from the tubing hanger; closingthe high-pressure valve; and removing the wireline lubricator.
 13. Themethod as claimed in claim 12, further comprising steps of: closing thehigh-pressure valve; disconnecting the high-pressure line; mounting thewireline lubricator to the top of the high-pressure valve; running inthe wireline to reset the plug in the production tubing; retrieving thewireline; removing the wireline lubricator; and removing the wellstimulation tool and the high-pressure valve from the tubing head spool.14. The method as claimed in claim 13, further comprising steps of:mounting a wellhead to the tubing head spool; mounting the wirelinelubricator to the wellhead; and running in the wireline to retrieve theplug.
 15. A method of stimulating a hydrocarbon well comprising stepsof: assembling a combination of a well stimulation tool and ahigh-pressure valve, the well stimulation tool comprising: an adapterspool having a bottom flange adapted for connection to a tubing headspool, and a top end adapted to receive a mandrel that can bereciprocally moved through packing that surrounds the mandrel and isretained in a packing cavity in the top end, the top end furtherincluding threads for securing a lockdown nut that covers the packingand surrounds an outer periphery of the mandrel; the mandrel having amandrel top end and a mandrel bottom end, the mandrel top end having aflange adapted for the connection of the high-pressure valve, and themandrel bottom end having a thread for the connection of an adapter pin;the adapter pin having an adapter pin top end and an adapter pin bottomend, the adapter pin top end having threads for connecting the adapterpin to the mandrel, and the adapter pin bottom end having threads forconnecting the adapter pin to a top of a tubing hanger in the tubinghead spool; and a lifting head assembly including a bottom end forconnection of the high-pressure valve and a top end with a lifting eyeto permit the well stimulation tool to be lifted for mounting to thetubing head spool; hoisting the combination of the well stimulation tooland the high-pressure valve above the tubing head spool of the well byconnecting to the lifting eye; lowering the combination to connect theadapter pin bottom end to the tubing hanger and further lowering thecombination to mount the adapter spool to the tubing head spool; andconnecting a high-pressure line to the high-pressure valve to permithigh-pressure fluids to be pumped into the hydrocarbon well.
 16. Themethod as claimed in claim 15, wherein prior to connecting thehigh-pressure line, the method further comprises steps of: disconnectingthe lifting head assembly from the high-pressure valve and the adapterspool after the adapter pin is connected to the tubing hanger and theadapter spool is mounted to the tubing head spool; and removing thelifting head assembly from the high-pressure valve.
 17. The method asclaimed in claim 16, further comprising steps of: mounting a wirelinelubricator to a top of the high-pressure valve; opening thehigh-pressure valve; running in a wireline and retrieving a plug fromthe production tubing; closing the high-pressure valve; and removing thewireline lubricator.
 18. The method as claimed in claim 17, furthercomprising steps of: closing the high-pressure valve; disconnecting thehigh-pressure line; mounting the wireline lubricator to the top of thehigh-pressure valve; opening the high-pressure valve; running in thewireline to reset the plug in the production tubing; retrieving thewireline; removing the wireline lubricator; and removing the combinationof the well stimulation tool and the high-pressure valve from the tubinghead spool.
 19. The method as claimed in claim 18, further comprisingsteps of: mounting a wellhead to the tubing head spool; mounting thewireline lubricator to the wellhead; and running in the wireline toretrieve the plug.
 20. The method as claimed in claim 18, wherein theremoval of the combination of the well stimulation tool and thehigh-pressure valve comprises steps of: hoisting the lifting headassembly back on the high-pressure valve; connecting the first member ofthe lifting head assembly to the high-pressure valve and connecting thesecond member of the lifting head assembly to the adapter spool;disconnecting the adapter spool from the tubing head spool; lifting thelifting head assembly to expose the adapter pin; disconnecting theadapter pin bottom end from the tubing hanger; and removing thecombination of the well stimulation tool and the high-pressure valve.